The invention relates to a method of creating a locating or load bearing surface having a desired flatness or profile.
Flat locating surfaces are required for a number of applications such as supporting guide ways for machine tools and for an optical scanning carriage in imagesetting machines. Conventionally, such a surface is obtained by precision machining a surface to the required level of flatness. The problem with this conventional approach is that for relatively long surfaces, for example 1.5 metres or more, the support member can bow for a number of reasons including temperature gradients, stress relief and machine tool errors.
U.S. Pat. No. 4,726,103 illustrates the use of an epoxy injection technique for locating guide ways in a predetermined relationship to each other on a bed of a machine tool. In this case, the guide ways are supported above the bed in precise locations and a bonding material is injected between the guide ways and the bed which then bonds the guide ways to the bed in their precise locations. This does not overcome the problems mentioned above since the load bearing surfaces would still need to have been machined to the desired degree of flatness, and the required degree of flatness or profile cannot be repeated precisely, using that technique.
In accordance with the present invention, a method of creating a locating or load bearing surface having a desired flatness or profile comprises
a) providing a base on which the surface is to be created;
b) locating a moulding member having a master surface with the desired flatness or profile facing and spaced from the base;
c) supplying a curable material to a region between the base and the master surface whereby the curable material contacts both the base and the master surface;
d) curing the curable material; and,
e) removing the moulding member so as to leave the surface having the desired flatness or profile provided on the exposed surface of the cured material.
With this invention, it is only necessary to use a known technique such as precision machining or hand finishing to obtain the desired flatness or profile on the master surface and thereafter that master surface can be used repeatedly to create corresponding surfaces on subsequent structures. It is therefore not necessary to use a conventional machining technique on each occasion on which a flat surface is required.
In some cases, the curable material will have sufficient viscosity to be retained between the master surface and the base prior to curing. An example of a suitable material is an epoxy.
Conveniently, however, the method further comprises providing a curable material confining wall around at least part of the said region. This could be defined by a wall of a recess provided in the base or alternatively the wall is made of a flexible material. This material would be provided on the base and is flexible so as not to affect the flatness or profile of the moulding member and thus the resultant locating or load bearing surface. There are various types of sealant which are suitable such as Tesomol, Poron, and rubber.
The base may have an elongate form and the curable material may be provided throughout the length of the base. In some applications, however, the base will have one or more upstanding bosses and in these cases the curable material will be provided on the bosses only.
In order to separate the master surface from the cured material in step e), the master surface may be treated to have the necessary release properties but conveniently the master surface is coated with a suitable release material. An example is Diamant Separator.
The moulding member may have any convenient form and may be in the form of a bar with a solid or box section.
The master surface will generally be flat but in some cases could have a profiled e.g. curved form. The precise form could be controlled by providing one or more micrometer adjusters along the moulding member. This would avoid the need for a high level of precision machining.
As mentioned previously, the invention has a number of applications but a particularly important application is in the construction of a guideway system for an optics carriage in an image setter, the method comprising creating a pair of substantially parallel, laterally spaced, elongate locating or load bearing surfaces using a method according to the invention.